The use of organic insulating layers is well known in the semiconductor processing art. Since organic insulators can be coated on substrates, they produce a degree of planarization not found in other thermally grown or vapor deposited insulating films. Moreover, organic insulating layers present film stresses which are compatible with metals such as aluminum/copper alloys, and thus they can be used to passivate the transistors, etc. formed on a semiconductor substrate.
These organic insulating layers must meet several relatively strict criteria. First, they should have the ability to passivate over topographical obstructions in a manner which results in stable adherent properties through subsequent high thermal exposures (e.g. 300.degree. C.-400.degree. C.). Second, the resulting film should be crack-free over all topographical steps. Third, these mechanically defect-free properties should not degrade through subsequent reliability stress conditioning (involving elevated temperature, humidity, and electrical bias) for more than 1000 hours.
More recently, a particular class of organic materials, referred to as "organosilanes", have been used in semiconductor applications.
In general, the use of organosilanes has been predominantly directed to promoting the adhesion of polyimide layers to underlaying layers. See e.g. U.S. Pat. No. 3,702,873, issued 11/14/72 to Hartlein.
U.S. Pat. No. 4,222,792 (issued 8/15/82 to Lever et al) discloses a method of forming filled isolation trenches utilizing an organosilane (i.e. polysiloxane). The isolation trenches are filled with a polymer consisting of alternating atoms of silicon and oxygen with organic groups attached to the silicon atoms, which is then E-beam exposed and developed. The polymer acts as a negative E-beam resist. The exposed polymer is then converted to SiO.sub.2 by heat treatment at 600.degree. C. in an oxygen furnace.
U.S. Pat. No. 4,430,153 (issued 2/7/84 to Gleason et al) discloses the formation of a reactive ion etch (RIE) barrier by coating an aromatic polyamic acid/imide on a silicon substrate, in-situ conversion of the polyamic acid to an alkyl polyamide/imide copolymer by exposure to an alkyl amino silicon compound, and selectively oxidizing portions of the copolymer to form an SiO.sub.2 etch barrier by exposure to a reactive ion etch in an oxygen atmosphere.
U.S. Pat. No. 4,349,609 (issued 9/14/82 to Takeda et al, discloses an organosiloxane polymer which is used as a passivation layer designed to provide a hermetic seal as well as a planarizing capability when applied over metal wiring patterns. A silsesquioxane solid is condensed from organosilane monomers that have a broad range of molecular weights (1000-1,000,000, preferably from about 1,500 to about 200,000). Such resulting glass resin solids (e.g. "GR#650" by Owens-Illinois Corp.) are commercially available in polymeric form with a molecular weight distribution of approximately 7000-20,000. Typically, these solids are spin-applied from a non-aqueous organic solvent such as n-butyl acetate.
Due to the relative low cost and adhesion promotion properties of such organosilanes, the inventors have investigated the use of hydrolyzed organoalkoxysilanes as organic insulating layers. This investigation resulted in the invention as described below.